Acta Trop 2025 Dec 02;272:107931. doi: 10.1016/j.actatropica.2025.107931.

Taxonomy and histopathology of Myxobolus mirandensis n. sp. parasite of the gills of Salminus brasiliensis from the Brazilian Pantanal wetland.

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Myxozoa are a highly diverse group of cnidarian parasites, with approximately 3070 described species. This study describes a new species, Myxobolus mirandensis n. sp., based on morphological, molecular, and histopathological analyses. The parasite was found in Salminus brasiliensis (dourado), one of the largest and most economically and recreationally important freshwater fish species in South America. Specimens of S. brasiliensis were collected from the Miranda River in the Brazilian Pantanal, with a prevalence of the infection of 63.6 % (7/11). White and elongated plasmodia were observed in the gill filaments. Pear-shaped myxospores measured 10.1 ± 0.3 µm in length, 6.6 ± 0.3 µm in width, and 5.1 ± 0.1 µm in thickness. Nematocysts were elongated and occupied more than half of the spore body, measuring 4.9 ± 0.3 µm in length and 1.9 ± 0.2 µm in width. Histopathological analysis revealed plasmodia developing in the epithelial tissue at the distal ends of the gill filaments, resulting in compression of adjacent tissues and structures. A thin connective tissue capsule surrounded the plasmodia, and numerous granulocytic cells were observed in the tissue adjacent to the plasmodia. Sequencing of the small subunit ribosomal DNA (SSU rDNA) yielded a 1954 bp fragment. Phylogenetic analysis showed M. mirandensis grouping with Myxobolus oliveirai and Myxobolus filamentum, both reported in Bryconidae hosts. This represents the seventh record of a myxozoan infecting S. brasiliensis.

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